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Summary: The woody stems of coniferous gymnosperms produce specialised compression wood to adjust the stem growth orientation in response to gravitropic stimulation. During this process, tracheids develop a compression‐wood‐specific S2L cell wall layer with lignins highly enriched with p‐hydroxyphenyl (H)‐type units derived from H‐type monolignol, whereas lignins produced in the cell walls of normal wood tracheids are exclusively composed of guaiacyl (G)‐type units from G‐type monolignol with a trace amount of H‐type units. We show that laccases, a class of lignin polymerisation enzymes, play a crucial role in the spatially organised polymerisation of H‐type and G‐type monolignols during compression wood formation in Japanese cypress (Chamaecyparis obtusa).We performed a series of chemical‐probe‐aided imaging analysis on C. obtusa compression wood cell walls, together with gene expression, protein localisation and enzymatic assays of C. obtusa laccases.Our data indicated that CoLac1 and CoLac3 with differential oxidation activities towards H‐type and G‐type monolignols were precisely localised to distinct cell wall layers in which H‐type and G‐type lignin units were preferentially produced during the development of compression wood tracheids.We propose that, not only the spatial localisation of laccases, but also their biochemical characteristics dictate the spatial patterning of lignin polymerisation in gymnosperm compression wood. [ABSTRACT FROM AUTHOR]

Winter is a critical season for land‐surface feedbacks and ecosystem processes; however, most high‐latitude paleo‐environmental reconstructions are blind to cold season conditions. Here we introduce a winter‐sensitive, paleo‐proxy record that is based on the relative frequency of tangential rows of traumatic resin ducts (TRDs) in the annual growth rings of mountain hemlocks (Tsuga mertensiana) growing near treeline in Southeast Alaska. Hemlocks produce a row of TRDs in the earlywood portion of their annual rings in response to cambial damage incurred during winter. Multidecadal bouts of TRD production were followed by growth‐leader replacement, reaction wood formation, and divergence in radial growth between storm‐damaged trees and less exposed mountain hemlock forests. These patterns are consistent with TRDs being a response to tree damage caused by ice and snowstorms, a conclusion supported by the krummholz tree architecture at these sites. This relationship is further corroborated by significant correlations between our TRD record and the strength of the wintertime Aleutian Low (AL) pressure system that is linked to tree‐damaging agents like wind, precipitation, and ice storm strength in Southeast Alaska. The combined TRD/krummholz architecture record indicates that abrupt shifts between strong and weak AL phases occurred every several decades since CE 1700 and that the 1800s had relatively long AL phases with heavy snowpacks. In addition to describing the magnitude and tempo of wintertime climate change in Northwestern North America, these results suggest that North Pacific Decadal Variability underlies the long‐term dynamics of treeline ecosystems along the northeast Pacific coast. Key Points: Traumatic resin ducts in the cross‐dated tree rings of subalpine mountain hemlocks record tree damage during winter storms in Southeast AlaskaWarmer, windier winters that accompany strong Aleutian Low pressure systems result in more tree damageDecadal‐scale variability in North Pacific climate has impacted treeline ecosystems throughout this region [ABSTRACT FROM AUTHOR]

PREMISE OF THE STUDY: Dimensions and spatial distribution of vessels are critically important features of woody stems, allowing for adaptation to different environments through their effects on hydraulic efficiency and vulnerability to embolism. Although our understanding of vessel development is poor, basipetal transport of auxin through the cambial zone may play an important role. METHODS: Stems of Populus tremula x alba were treated with the auxin transport inhibitor N-1- naphthylphthalamic acid (NPA) in a longitudinal strip along the length of the lower stem. Vessel lumen diameter, circularity and length; xylem growth; tension wood area and hydraulic conductivity before and after a high pressure flush were determined on both NPA-treated and control plants. KEY RESULTS: NPA-treated stems formed aberrant vessels that were short, small in diameter, highly clustered and angular in cross section, whereas xylem formed on the untreated side of the stem contained typical vessels that were similar to those of controls. NPA-treated stems had reduced specific conductivity relative to controls, but this difference was eliminated by the high-pressure flush. The control treatment (lanolin + dimethyl sulfoxide) reduced xylem growth and increased tension wood formation, but never produced the aberrant vessel patterning seen in NPA-treated stems. CONCLUSIONS: These results are consistent with a model of vessel development in which basipetal polar auxin transport through the xylem-side cambial derivatives is required for proper expansion and patterning of vessels and demonstrate that reduced auxin transport can produce stems with altered stem hydraulic properties. [ABSTRACT FROM AUTHOR]

Contents790I.790II.792III.795IV.797V.798VI.800VII.800800References800 Summary: The woody stems of trees perceive gravity to determine their orientation, and can produce reaction woods to reinforce or change their position. Together, graviperception and reaction woods play fundamental roles in tree architecture, posture control, and reorientation of stems displaced by wind or other environmental forces. Angiosperms and gymnosperms have evolved strikingly different types of reaction wood. Tension wood of angiosperms creates strong tensile force to pull stems upward, while compression wood of gymnosperms creates compressive force to push stems upward. In this review, the general features and evolution of tension wood and compression wood are presented, along with descriptions of how gravitropisms and reaction woods contribute to the survival and morphology of trees. An overview is presented of the molecular and genetic mechanisms underlying graviperception, initial graviresponse and the regulation of tension wood development in the model angiosperm, Populus. Critical research questions and new approaches are discussed. [ABSTRACT FROM AUTHOR]

Tension wood has distinct physical and chemical properties, including altered fibre properties, cell wall composition and ultrastructure. It serves as a good system for investigating the genetic regulation of secondary cell wall biosynthesis and wood formation. The reference genome sequence for Eucalyptus grandis allows investigation of the global transcriptional reprogramming that accompanies tension wood formation in this global wood fibre crop., We report the first comprehensive analysis of physicochemical wood property changes in tension wood of Eucalyptus measured in a hybrid ( E. grandis × Eucalyptus urophylla) clone, as well as genome-wide gene expression changes in xylem tissues 3 wk post-induction using RNA sequencing., We found that Eucalyptus tension wood in field-grown trees is characterized by an increase in cellulose, a reduction in lignin, xylose and mannose, and a marked increase in galactose. Gene expression profiling in tension wood-forming tissue showed corresponding down-regulation of monolignol biosynthetic genes, and differential expression of several carbohydrate active enzymes., We conclude that alterations of cell wall traits induced by tension wood formation in Eucalyptus are a consequence of a combination of down-regulation of lignin biosynthesis and hemicellulose remodelling, rather than the often proposed up-regulation of the cellulose biosynthetic pathway. [ABSTRACT FROM AUTHOR]

We studied in detail the mean microfibril angle and the width of cellulose crystals from the pith to the bark of a 15-year-old Maidenhair tree ( Ginkgo biloba L.). The orientation of cellulose microfibrils with respect to the cell axis and the width and length of cellulose crystallites were determined using X-ray diffraction. Raman microscopy was used to compare the lignin distribution in the cell wall of normal/opposite and compression wood, which was found near the pith. Ginkgo biloba showed a relatively large mean microfibril angle, varying between 19° and 39° in the S2 layer, and the average width of cellulose crystallites was 3.1-3.2 nm. Mild compression wood without any intercellular spaces or helical cavities was observed near the pith. Slit-like bordered pit openings and a heavily lignified S2L layer confirmed the presence of compression wood. Ginkgo biloba showed typical features present in the juvenile wood of conifers. The microfibril angle remained large over the 14 annual rings. The entire stem disc, with a diameter of 18 cm, was considered to consist of juvenile wood. The properties of juvenile and compression wood as well as the cellulose orientation and crystalline width indicate that the wood formation of G. biloba is similar to that of modern conifers. [ABSTRACT FROM AUTHOR]

* Premise of the study: Reaction wood (RW) in seed plants can induce late and usually secondary changes in organ orientation. Conifers produce compression wood (CW), generated by compression tracheids, which generate a push force. Angiosperms produce tension wood (TW), generated by tension wood fibers (TWF) often described as "gelatinous fibers," which exert a pull force. Usually RW is produced eccentrically, but it can occur concentrically, as in aerial roots of Ficus. However, gymnosperms can produce gelatinous fibers (tension fibers, TF), as in cortical and secondary phloem tissues (Gnetum). TFs are therefore limited neither to wood, xylem, nor angiosperms. Here we demonstrate that TFs in secondary phloem are involved in contraction of roots of cycads and compare them with TFs of Ficus. * Methods: We sectioned root material of cycads at various stages of seedling development using simple staining and histochemical procedures to follow the course of secondary phloem development. Aerial roots of Ficus were compared with the cycad root material. * Key results: Tension fibers (gelatinous fibers) occur extensively and continuously in the secondary phloem in roots that undergo contraction. Older tissues, but notably the xylem, become distorted by contraction. TFs in cycads correspond in cell wall features to TFs that occur in Ficus, but do not occur in secondary xylem. The individual fibers visibly contract. * Conclusions: Tissue contraction in Cycas and Zamia corresponds to that found in angiosperms and Gnetum and further broadens the scope of the activity of tension tissues. This finding possibly indicates that gelatinous fibers originated at a very early period of seed plant evolution. [ABSTRACT FROM AUTHOR]

Premise of the study: Some of the most striking stem shapes occur in species of Bauhinia (Fabaceae) known as monkey ladder vines. Their mature stems are flattened and develop regular undulations. Although stems have variant (anomalous) secondary growth, the mechanism causing the undulations is unknown. Methods: We measured stem segments over time (20 mo), described stem development using light microscopy, and correlated the changes in stem shape with anatomy. Key results: Growing stems are initially straight and bear tendrils on short axillary branches. The inner secondary xylem has narrow vessels and lignified fibers. As stems age, they become flattened and increasingly undulated with the production of two lobes of outer secondary xylem (OX) with wide vessels and only gelatinous fibers (G-fibers). Similar G-fibers are present in the secondary phloem and the cortical sclerified layer. In transverse sections, the concave side of each undulation has a greater area and quantity of G-fibers than the opposite convex side. Some older stems are not undulated and have less lobing of OX. Undulation causes a shortening of the stem segments: up to 28% of the original length. Conclusions: Uneven distribution of G-fibers produces tensions that are involved in the protracted development of undulations. While young extending shoots attach by lateral branch tendrils, older stems may maintain their position in the canopy using undulations and persistent branch bases as gripping devices. Flattened and undulated stems with G-fibers produce flexible woody stems. [ABSTRACT FROM AUTHOR]

Ethylene Response Factors (ERFs) are a large family of transcription factors that mediate responses to ethylene. Ethylene affects many aspects of wood development and is involved in tension wood formation. Thus ERFs could be key players connecting ethylene action to wood development., We identified 170 gene models encoding ERFs in the Populus trichocarpa genome. The transcriptional responses of ERF genes to ethylene treatments were determined in stem tissues of hybrid aspen ( Populus tremula × tremuloides) by qPCR. Selected ethylene-responsive ERFs were overexpressed in wood-forming tissues and characterized for growth and wood chemotypes by FT-IR., Fifty ERFs in Populus showed more than five-fold increased transcript accumulation in response to ethylene treatments. Twenty-six ERFs were selected for further analyses. A majority of these were induced during tension wood formation. Overexpression of ERFs 18, 21, 30, 85 and 139 in wood-forming tissues of hybrid aspen modified the wood chemotype. Moreover, overexpression of ERF139 caused a dwarf-phenotype with altered wood development, and overexpression of ERF18, 34 and 35 slightly increased stem diameter., We identified ethylene-induced ERFs that respond to tension wood formation, and modify wood formation when overexpressed. This provides support for their role in ethylene-mediated regulation of wood development. [ABSTRACT FROM AUTHOR]

Wood cell walls fluoresce as a result of UV and visible light excitation due to the presence of lignin. Fluorescence spectroscopy has revealed characteristic spectral differences in various wood types, notably normal and compression wood. In order to extend this method of characterising cell walls we examined the fluorescence lifetime of wood cell walls using TCSPC (Time-Correlated Single Photon Counting) as a method of potentially detecting differences in lignin composition and measuring the molecular environment within cell walls. The fluorescence decay curves of both normal and compression wood from pine contain three exponential decay components with a mean lifetime of τm = 473 ps in normal wood and 418 ps in compression wood. Lifetimes are spatially resolved to different cell wall layers or cell types where individual lifetimes are shown to have a log-normal distribution. The differences in fluorescence lifetime observed in pine compression wood compared to normal wood, are associated with known differences in cell wall composition such as increased p-hydroxyphenyl content in lignin as well as novel deposition of β(1,4)-Galactan. Our results indicate increased deposition of lignin fluorophores with shorter lifetimes in the outer secondary wall of compression wood. We have demonstrated the usefulness of fluorescence lifetime imaging for characterising wood cell walls, offering some advantages over conventional fluorescence imaging/spectroscopy. For example, we have measured significant changes in fluorescence lifetime resulting from changes to lignin composition as a result of compression wood formation that complement similar changes in fluorescence intensity. [ABSTRACT FROM AUTHOR]

* Premise of the study: Gravitropic movements are unexpected mechanical processes that could disturb tree design allometries derived from the physics of nonliving bodies. We investigated whether the scaling law of gravitropic performance (power of --2 of stem diameter) derived from integrative biomechanical modeling is disturbed by ontogeny or environment, then discuss the silvicultural and dendroecological consequences. * Methods: In a beech (Fagus sylvatica) plantation, four plots with different initial planting densities evolved without any intervention for 26 yr. Regular tree inventories and a silvicultural model were used to monitor competition over time in each plot. The radial production of tension wood was quantified using a cross-section of the stems at 1.30-m height, and an integrative biomechanical model computed the tree gravitropic performance over time. * Key results: All trees developed tension wood over the whole period, with higher amounts at the youngest age, resulting in theoretical lean corrections of ca. 20-30° on the first 4 m of the stem over the whole period. The scaling law of gravitropic performance is slightly larger than the power of --2 of stem diameter. * Conclusions: Gravitropic performance in forest ecosystems is mainly limited by size (diameter). Ontogenic acclimation of tension wood formation allows the youngest trees to be more reactive. No additional effect of spacing was found. However, silviculture influences size and, therefore, tree reactivity at a given age. Such results will be helpful for dendroecological approaches that use wood as a marker of environmental disturbances or a trait linked to plant strategies. [ABSTRACT FROM AUTHOR]

Compression wood (CW) is a reaction wood formed in gymnosperms in response to various growth stresses. Many of the anatomical, chemical, physical, and mechanical properties of CW differ distinctly from those of normal wood. Because of different properties, the CW is much less desirable than normal wood. This study was conducted to investigate the suitability of CW flour obtained from black pine ( Pinus nigra Arnold) in the manufacture of wood plastic composite (WPC). Polypropylene (PP) and CW flour were compounded into pellets by twin-screw extrusion, and the test specimens were prepared by injection molding. WPCs were manufactured using various weight percentages of CW flour/PP and maleic anhydride-grafted PP (MAPP). Water absorption (WA), modulus of rupture (MOR), and modulus of elasticity (MOE) values were measured. The results showed that increasing of the CW percentage in the WPC increased WA, MOR, and MOE values. Using MAPP in the mixture improved water resistance and flexural properties. CW flour of black pine can be used for the manufacturing of WPC as a reinforcing filler. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

Reaction wood possesses altered properties and performs the function of regulating a tree's form, but it is a serious defect in wood utility. Trees usually develop reaction wood in response to a gravistimulus. Reaction wood in gymnosperms is referred to as compression wood and develops on the lower side of leaning stems or branches. In arboreal, dicotyledonous angiosperms, however, it is called tension wood and is formed on the upper side of the leaning. Exploring the biology of reaction wood formation is of great value for the understanding of the wood differentiation mechanisms, cambial activity, gravitropism, and the systematics and evolution of plants. After giving an outline of the variety of wood and properties of reaction wood, this review lays emphasis on various stimuli for reaction wood induction and the extensive studies carried out so far on the roles of plant hormones in reaction wood formation. Inconsistent results have been reported for the effects of plant hormones. Both auxin and ethylene regulate the formation of compression wood in gymnosperms. However, the role of ethylene may be indirect as exogenous ethylene cannot induce compression wood formation. Tension wood formation is mainly regulated by auxin and gibberellin. Interactions among hormones and other substances may play important parts in the regulation of reaction wood formation. [ABSTRACT FROM AUTHOR]

ABSTRACT Compression wood is formed at the underside of conifer twigs to keep branches at their equilibrium position. It differs from opposite wood anatomically and subsequently in its mechanical and hydraulic properties. The specific hydraulic conductivity (k s ) and vulnerability to drought-induced embolism (loss of conductivity versus water potential ψ ) in twigs of Norway spruce [Picea abies (L.) Karst.] were studied via cryo-scanning electron microscope observations, dye experiments and a newly developed ‘Micro-Sperry’ apparatus. This new technique enabled conductivity measurements in small xylem areas by insertion of syringe cannulas into twig samples. The hydraulic properties were related to anatomical parameters (tracheid diameter, wall thickness). Compression wood exhibited 79% lower k s than opposite wood corresponding to smaller tracheid diameters. Vulnerability was higher in compression wood despite its narrower tracheids and thicker cell walls. The P50 (ψ at 50% loss of conductivity) was -3.6 MPa in opposite but only -3.2 MPa in compression wood. Low hydraulic efficiency and low hydraulic safety indicate that compression wood has primarily a mechanical function. [ABSTRACT FROM AUTHOR]

Summary • Compression wood has been shown to reduce stem permeability, but it is not known to what extent it affects leaf-level processes. Here, we report whole-plant hydraulic properties of Douglas-fir (Pseudotsuga menziesii ) seedlings induced to form varying amounts of compression wood. • Seedlings were grown under three bending treatments to assess the impact of compression wood on hydraulic properties, including stomatal conductance (g s ), above-ground shoot conductance (K l(abg) ), and both specific and leaf area-specific conductivity (k s and k l , respectively). • K l(abg) was significantly lower (50% reduction) in severely bent seedlings than in controls. Similarly, both k s and k l of the main axis were significantly reduced (by 52% and 46%, respectively) in severely bent seedlings relative to controls. Seedlings in the moderate bending treatments had k s and k l that were intermediate between controls and severe bending. • Despite clear differences in above-ground shoot hydraulic properties, severely bent seedlings maintained the same water potentials as controls and had similar diurnal patterns of g s . This suggests that when the entire soil–plant–atmosphere continuum is considered, even a severe reduction in stem k s caused by compression wood has little impact on leaf-level processes. [ABSTRACT FROM AUTHOR]

In most gymnosperms, resistance to the flow of water per unit path length through the main stem is less than that of lateral branches. Using branches, leaders, and branches that have replaced missing leaders (‘branch-leaders’), we tested the hypothesis that branch-leaders are at a hydraulic disadvantage. Reduced xylem transport efficiency in branch-leaders relative to leaders could be expected both because of an initial disparity in hydraulic capacity, and because of the relatively impermeable compression wood formed in branch-leaders during shoot reorientation. By subsampling branch-leaders, we also tested the hypothesis that opposite wood (formed directly opposite compression wood) is more permeable than normal wood, and could, therefore, compensate for the presence of compression wood at the whole shoot level. Fifteen months after leader removal, branch-leaders were intermediate between branches and leaders in their ability to supply foliage with water, suggesting a transition towards leader status that was not yet complete. Increased hydraulic capacity in branch-leaders was the result of increased xylem cross-sectional area per unit foliage, rather than an increase in permeability. Among subsampled wood types from basal branch-leader segments, opposite wood was significantly less permeable than normal wood, suggesting that it does not compensate for the presence of compression wood. [ABSTRACT FROM AUTHOR]

In this contribution, a micromechanical modeling approach in the framework of poromechanics is adopted to study structure-stiffness relations of two quite different species, namely spruce and yew, in detail. In particular, microstructural specialties of yew and spruce are assessed. A dominant influence of the cellulose content and its orientation on the stiffness of the cell wall is revealed, while on the macroscopic scale, density is found to be the governing microstructural characteristic for elastic properties. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]